1. Field of the Invention
The invention relates generally to optical nondestructive testing methods and optical nondestructive testing apparatuses. More particularly, the invention relates to an optical nondestructive testing method and an optical nondestructive testing apparatus that optically nondestructively determine a connection area between connection interfaces of a first member and a second member of a measurement object connected to each other directly or connected to each other with a connector interposed therebetween.
2. Description of the Related Art
In recent years, first and second members made of various materials have been connected to each other, creating a demand for testing the state of connection between the first and second members. A conventional method for testing the state of connection involves selecting an appropriate sample from a production lot, and breaking the sample so as to check the state of connection. Thus, products in this lot are regarded as having the state of connection similar to the state of connection of the sample broken. This conventional method unfortunately requires breaking a sample in order to check the state of connection. To overcome this disadvantage, various methods are disclosed to measure connection-related physical properties without causing breakage.
U.S. Pat. No. 7,364,354 discloses a thermal diffusivity measuring method involving applying a modulated beam to a measurement spot of a unitary sample so as to determine the thermal diffusivity of the sample on the basis of the phase of the modulated beam and the phase of a temperature response from the measurement spot.
Japanese Patent Application Publication No. 2002-122559 (JP 2002-122559 A) discloses a method for measuring thermal diffusivity and interfacial thermal resistance. This method involves: providing a three-layer structure made up of upper and lower metallic thin film layers of the same type having known thermophysical property values and a nonmetallic thin film layer sandwiched between the upper and lower metallic thin film layers and having unknown thermophysical property values; heating the three-layer structure from below with pulsed light; and measuring a transient temperature rise at the upper surface of the three-layer structure. Thus, the thermal diffusivity and interfacial thermal resistance of the three-layer structure are measured simultaneously.
Japanese Patent No. 3265362 discloses an interfacial thermal resistance measuring method involving: pulse-heating the surface of a two-layer sample provided by stacking a first layer made of a first material and a second layer made of a second material; and observing a temperature response from the underside of the two-layer sample. Thus, interfacial thermal resistance between the first and second layers of the two-layer sample is measured. Japanese Patent No. 3265362 also discloses an interfacial thermal resistance measuring method involving: measuring a temperature response after pulse-heating the surface of a first single layer sample consisting of a first material; measuring a temperature response after pulse-heating the surface of a second single layer sample consisting of a second material; and calculating a temperature response on the assumption that no interfacial thermal resistance is generated between the first and second layers of a two-layer sample that are made of the first and second materials, respectively, and stacked one on top of another. This method further involves determining a difference between the temperature response calculated and a temperature response from the underside of the two-layer sample measured after pulse-heating the surface of the two-layer sample. Thus, interfacial thermal resistance between the first and second layers of the two-layer sample is determined from the difference between the temperature responses.
The invention disclosed in U.S. Pat. No. 7,364,354 aims at measuring the thermal diffusivity of a unitary sample but does not aim at measuring the thermal diffusivity of a connector connecting a first member and a second member. This means that the thermal diffusivity measured is unusable for determining the state of connection between first and second members of a measurement object connected to each other directly or connected to each other with a connector interposed therebetween.
The invention disclosed in JP 2002-122559 A is applicable only to a three-layer structure made up of upper and lower metallic thin film layers of the same type having known thermophysical property values and a nonmetallic thin film layer sandwiched between the upper and lower metallic thin film layers. The physical properties to be measured are the thermal diffusivity and interfacial thermal resistance of the three-layer structure. This makes it inappropriate to apply this invention to determining the state of connection between the first and second members of a measurement object connected to each other directly or connected to each other with a connector interposed therebetween.
The invention disclosed in Japanese Patent No. 3265362 requires pulse-heating the surface of a sample and measuring a temperature response from the underside of the sample. This means that heat has to be sufficiently propagated from the surface of the sample to the underside of the sample. Thus, this invention is applicable only to a sample in the form of a thin film. The physical property to be measured is the interfacial thermal resistance of a two-layer sample. This makes it inappropriate to apply this invention to determining the state of connection between the first and second members of a measurement object connected to each other directly or connected to each other with a connector interposed therebetween.